llegal, but socially acceptable stuff:
Marijuana: Non-addictive. Yeah, it's fun, and it's easy to smoke every day, but this is extremely easy to quit. You don't smoke in bars (in most countries), and very few (good) jobs allow you to have this kind of smoke break. I smoked heavily from 18 until I moved to Japan (23-ish), at which point it became a social thing. Marijuana DOES affect your short-term memory, but it comes back when you quit smoking. You *CAN* drive after being extremely baked. If you can't, you're doing something wrong. Driving while your'e really really high is like driving when you've just woken up. Not the safest, but nowhere near as dangerous as when drunk. You're usually going 10 mph under the speed limit anyway. Am I wrong? Someone please post me a link to the "Dont smoke pot and drive" web page, or a link to an accident where someone was ONLY smoking pot and wrecked their car?
Hallucinogens (Acid, Mushrooms) These are the most non-addictive drugs. They last so fucking long and are so intense, you don't want to touch them when they're done. I do not recommend driving on these. I also don't recommend being around people you don't trust, as it can really freak you out. These do NOT make you think you can fly, jump out of buildings, jump in front of cars, etc. Only when coupled with a pre-established mental condition does shit like that happen. In fact, to TRULY hallucinate (IE, talk to elves and shit) you have to eat a lot of really strong stuff, and it takes agse to come back to reality. Truly a college thing.
MDMA (Ecstacy): Very fun, and the only thing I really miss from my younger days. It's a low grade amphetimine (speed) which is why your heart speeds up and you tend to dehydrate. On that note, it's the dehydration that kills you - not the MDMA. If you're going to dance in a sweaty club w/ no AC - drink some water like a human. No long term side effects have been proven but it's pretty obvious it does some bad shit. Nothing feels that good without a price. Short term effects (in terms of days, weeks) is very noticeable. Memeory loss, massive appetite loss, depression a few days later, not to mention some nasty funk in your saliva. Yes, it does make you very horny, but does something w/ your urinary tract, so peeing, and achieving orgasm (for men) can prove difficult. Length of this difficulty depends on how many you eat.